This invention relates to a machine tool for machining a workpiece, for example, a printed circuit board, and more particularly to a tool detecting apparatus for detecting a tool such as a drill or an end mill held on a spindle.
The position of a tool used in a machine tool is commonly detected by bringing a probe of a detector into contact with the tip of the tool.
For the purpose of detection of a small tool such as that used in a drilling machine for drilling holes in printed circuit boards, various tool detecting apparatus were proposed, and, as an example of such prior art apparatus, it was proposed to use an optical type detector, as disclosed in U.S. Pat. No. 4,658,494.
However, all of these prior art tool detecting apparatus were designed to detect the position of the tip of a tool, and the accuracy of detection was limited.
With the increasing production of a variety of kinds of printed circuit boards, a variety of kinds of machining have been required for the printed circuit boards, and machining with high accuracy has been increasingly demanded.
For example, in the case of drilling a blind hole or milling a groove in a printed circuit board, a depthwise accuracy as high as about .+-.20 .mu.m is now demanded.
Also, in the case of drilling through holes in a printed circuit board, drilling of a variety of kinds of diameters between 0.1 mm and 6.3 mm with an increment of 0.1 mm is now demanded, and, as a result, management for supplying such many kinds of drills becomes complex.
Therefore, it has been desired to detect, with high accuracy, the tip position, diameter or eccentricity of a tool supplied to a spindle of a machine tool to effect machining which meets desired machining requirements.